Chlorine is a useful material for vinyl chloride and phosgene. Chlorine is mainly produced by brine electrolysis or catalytic oxidation of hydrogen chloride.
Brine electrolysis entails a great amount of electricity and is disadvantageous in terms of energy. It also generates sodium hydroxide as a by-product, and therefore the balance between the products has to be considered.
In the catalytic oxidation of hydrogen chloride, hydrogen chloride that is a material is a by-product from the production of vinyl chloride or phosgene. Therefore, this process is advantageous in view of effective use of by-products.
The catalytic oxidation of hydrogen chloride into chlorine is an exothermic reaction. The equilibrium conversion is dependent on temperature, and the reaction is more advantageous when carried out at lower temperatures. For use in this reaction, Deacon catalysts based on copper, Cr2O3/SiO2 catalyst and RuO2/TiO2 catalyst are known (for example, Patent Document 1).
Known copper-based Deacon catalysts include catalysts in which copper chloride, an alkali metal chloride and a lanthanoid such as didymium chloride are supported on a silica gel carrier with a specific surface area of not less than 200 m2/g and an average pore diameter of not less than 60 Å (for example, Patent Document 2), and fluidized bed catalysts in which copper, potassium and didymium are impregnated in a silica gel having a specific surface area of 410 m2/g and a pore volume of 0.72 ml/g (for example, Patent Document 3).
These catalysts, however, have both merits and demerits. The Deacon catalysts and Cr2O3/SiO2 catalyst have inexpensive active components, but their activity is insufficient and the reaction has to be made at high temperatures. The oxidation of hydrochloric acid is exothermic, and the reaction equilibrium gives a lower conversion at a higher temperature. The RuO2/TiO2 catalyst has high activity and can catalyze the reaction even if it is supported in a small amount. However, it is necessary that the noble metal should be recovered and recycled from the exhausted catalyst. Furthermore, Ru has become more expensive due to recent increase in demands. Thus, this catalyst is disadvantageous in view of stable supply and costs.
The didymium is a mixture containing various rare earth elements. The mixture has a different composition depending on the place and time where it is mined. Accordingly, catalysts containing didymium show varied activity and do not provide stable performance.
Thus, there is a demand for catalysts that have inexpensive and stably supplied components and can catalyze a reaction at lower temperatures.    [Patent Document 1] JP-A-H09-67103    [Patent Document 2] U.S. Pat. No. 3,260,678    [Patent Document 3] U.S. Pat. No. 3,483,136